Are "upcalls" supported?

[chris-asl]

I want to use libp2p-kad-dht as a DHT for an application.
I am wondering if there's a way to inform this application for new keys about to be saved (or even saved already), i.e. if upcalls are supported.

Example:
Given 3 nodes, A, B and C, that run my application which uses libp2p-kad-dht.

Given a put(keyX, valueY) issued by the application of node A and that the value should be stored in node C, is there a way for informing the application of node C, that a <key, value> is about to be stored?

[vasco-santos]

Hello @chris-asl

Thanks for reaching out. We currently do not support that use case with upcalls. However, I am willing to discuss a proposal for implementing it.

[chris-asl]

@vasco-santos thanks for the reply!
In the meantime I have been digging around the code, and was thinking whether the validators, which if I got this right, run at each node that stores the value, can be used as upcalls.

Thus, allowing the application on top of libp2p-kad-dht decide whether or not to save the value (probably by cb(Error('no store')) from the validator).

[vasco-santos]

So, the validator is responsible for validating if the record is valid under certain conditions (we receive a function). The selector is responsible for selecting which occurrence from a record is the best one.

At a first glimpse, I believe that we could add a new function parameter, such as the validator and selector that could notice upwards that a key was stored (I am not sure about a good naming yet). This sounds a reasonable approach as we would only notice if the application adds that function, and consequently, only who wants to use this will use.